1. Field of the Invention
The invention is related to dental repair materials. Specifically improved MTA (mineral trioxide aggregate) with improved handling and sealing properties.
2. Summary of the Related Art
Various compounds have been used as dental fill materials for cavities and root canal therapy. These include Amalgam, Reinforced Zinc Oxide-Eugenol (IRM and Super EBA), Composite Resins and Mineral Trioxide Aggregate (MTA) and Portland Cement, herein after referred to generally as “Dental Repair Compound”.
The attributes generally sought for root-end filling material include the ability to 1) seal the apical portion in three dimensions, 2) be well tolerated by the periradicular tissues with no inflammatory reactions, 3) be non-toxic, 4) not promote, and preferably inhibit, the growth of pathogenic organisms, 5) stimulate the regeneration of normal repiradicular tissues, 6) not be affected by moisture in either the set or unset state, 7) not be absorbable by the body within the confines of the tooth, but excess should be absorbable, 8) be dimensionally stable and should not expand, contract, or flow in any direction when set, 9) not corrode or be electrochemically active, 10) not stain the tooth or the periradicular tissues, 11) be easy to mix and insert, 12) be easily distinguishable on radiographs, and 13) adhere or bond to the tooth without the need of undercuts.
MTA has been demonstrated to have diverse applications for all fields of dentistry and appears to fulfill most characteristics of an ideal cement due to its unique properties such as tissue compatibility, marginal adaptation, sealing ability, hydrophilic properties, and the capacity to stimulate hard tissue formation. These properties have allowed MTA to be indicated for the following endodontic procedures: Pulp Capping, Apexification, Perforation repair and other Miscellaneous uses.
Pulp Capping—In 1929, Hess reported a pulpotomy technique using calcium hydroxide. Until recently, these calcium hydroxide-based materials have found widespread use in traditional vital pulp therapy and have been the mainstay for the protection of exposed dental pulps. The healing process of the dental pulp following a pulpotomy or a direct pulp cap is characterized by the formation of a hard tissue bridge with the maintenance of a vital subjacent pulp tissue free from chronic inflammatory cells. Recently, MTA has been approved by the FDA and recommended for direct pulp capping. MTA's mechanism of action is thought to be similar to that of calcium hydroxide. MTA has calcium oxide that mixes with water to form calcium hydroxide. The reaction of the calcium from the calcium hydroxide with the carbon dioxide from the pulp tissue produces calcite crystals. These calcite crystals are thought to be the initiating factor in the induction of a hard tissue barrier. Seux (1) observed a rich extracellular network of fibronectin in close contact with these crystals and concluded that both were integral in the initiating steps in the formation of a hard tissue barrier. Tziafas (2) concluded that MTA was able to induce cytological and functional changes in pulpal cells, resulting in the formation of fibrodentin at the surface of a mechanically exposed dental pulp.
Human studies have shown MTA to cause less pulpal hyperemia, inflammation, and necrosis when compared to calcium hydroxide. In a study performed by Aeinehchi, (7) MTA induced a thicker dentinal bridge in third molars and was found to be associated with an intact odontoblastic layer more often than with calcium hydroxide. Additional reasons MTA is an effective pulp capping material is its ability to effectively seal the dentin-material interface to prevent bacterial contamination, it is nonresorbable, proven biocompatibility, and beneficial alkaline properties (25; 26; 27). Because of this, MTA is also recommended for treatment of traumatically exposed pulps for the treatment of complicated crown fractures (8).
Apexification—The traditional protocol in the treatment of necrotic immature teeth is through apexification using calcium hydroxide. In 1959, Granath was the first to describe the utilization of calcium hydroxide for apical closure. In 1966, Frank mainstreamed the apexification technique and was credited as being the first to use this modality (9). This methodology consists of multiple appointments exchanging calcium hydroxide as the intracanal medicament to induce an apical hard tissue barrier ultimately to control the root canal filling material. The calcium hydroxide is changed every 3 months until there is evidence of apical barrier formation. The most important problem with the classic apexification technique with calcium hydroxide is the duration of therapy, which can last from 3 to 24 months (9; 10). During this time frame the root canal is susceptible to reinfection due to the difficulty in maintaining a temporary restorative material that adequately seals the access opening. The root is also at risk to fracture due to the long treatment time required for apical barrier formation.
MTA treatment of these cases allows for a single treatment of immature teeth as an option. The MTA apical plug technique, a one-step obturation after short canal disinfection with calcium hydroxide is designated to create an artificial stop to the filling material. The physical characteristics of MTA provide advantages over the traditional calcium hydroxide technique. MTA apexification cases can be restored in approximately two weeks as opposed to traditional calcium hydroxide therapy, which could take several months. MTA provides excellent marginal adaptation to prevent leakage and the material is non-resorbable. In 1996, Buchanan first recommended the use of MTA for one-appointment apexification by placing an apical matrix of freeze-dried demineralized bone followed by condensation of MTA (11). Witherspoon also recommends a technique for one-visit apexification. This technique advocates filling the apical to middle third with MTA, with the remainder of the canal system to be restored with a core material to reinforce the thin walls of the root (12). Giuliani described using MTA as an apical plug in teeth with necrotic pulps and open apices. His technique advocated the use of calcium hydroxide treatment for one week prior to placement of MTA as an apical plug with subsequent obturation of the canal system. At recall, the clinical symptoms and teeth with periapical lesions had resolution within 6-12 months (13). Hachmeister, in an MTA displacement study, concluded there was a significant greater resistance to force with a 4 mm thickness of MTA, regardless of calcium hydroxide use. Thus, the ideal recommended thickness of the apical plug was shown to be 4 mm, in order to resist displacement of the material (14).
Perforation Repair—In dentistry, procedural accidents such as root or furcal perforations can occur during root canal therapy, post space preparation, or as a consequence of internal resorption. Studies have shown that these perforations predispose periradicular tissues to chronic inflammation and promote the advancement of periodontal attachment loss, ultimately causing the loss of the tooth (15). Ingle reported that perforations were the second greatest cause of endodontic failure and accounted for 9.6% of all unsuccessful cases (16).
The repair of perforations can be problematic due to extrusion of the repair filling material, improper hemorrhage control, and the ability of the material to adequately seal the perforation site. MTA's unique physical characteristics allowing for superior marginal adaptation and sealing ability in hematic environments along with its osteo/cementoconductive attributes make it an excellent material for perforation repair (28; 29; 30; 31). The inherent hydrophilic properties of MTA allow the repair material to set in a wet environment and adequately seal the perforation site. In 1993, Lee reported the first in vitro study investigating the sealing ability of MTA for repair of lateral root perforations. The authors were able to demonstrate that moisture of the surrounding tissue acted as an activator of the chemical reaction and did not pose a risk with its use in a moist environment. They were also able to demonstrate that overextrusion of the material into the perforation site occurred mostly in the IRM group, followed by the amalgam group and then MTA. Lee concluded that the hydrophilic powder absorbs moisture and allows for minimal condensation force, thus decreasing the chance of overextrusion of the material (49). Sluyk concluded that the presence of moisture in the perforation site during placement was advantageous in aiding adaptation of MTA to the walls of the perforation (86).
Histologic repair of the perforation is possible with MTA. Pitt Ford et al. demonstrated using an in vitro canine model, that cementum has been was produced over MTA repairing perforations in the absence of inflammation. Based on these results, Pitt Ford recommended the use of MTA for immediate perforation repair (19). Holland also demonstrated no inflammation associated with repair of lateral root perforations with MTA over a 180 day observation period and that there was evidence of cementum deposition in the majority of specimens (20). Recent studies performed to evaluate the clinical efficacy of MTA to seal both furcal and lateral perforations have only validated MTA as the material of choice in perforation repair (88-90).
Miscellaneous Uses—Additional uses for MTA have also been suggested. In a study performed by Cummings, MTA was compared to other materials and evaluated as an isolating barrier for internal bleaching. MTA demonstrated the least amount of leakage compared to IRM and zinc phosphate. It was concluded that this material can be used as an effective isolating barrier for internal bleaching (21).
There have been several case reports documenting alternative uses for MTA. Hsiang-Chi presented a successful case report demonstrating the repair of perforating internal resorption with MTA. A partial pulpotomy was performed, and the material was placed adjacent to the exposed pulp. Teeth were extracted after 6 months. Histological exam of the teeth showed continuous dentin bridge formation without inflammation 6 months after initial treatment (93). O'Sullivan (23), in another case report, demonstrated obturation of the canal system with MTA in a retained primary mandibular second molar where there was no succendaneous tooth present. Eidelman et al. found clinical and radiographic success as a dressing material following pulpotomy in primary teeth, suggesting MTA as a possible alternative to formocresol in primary teeth (24).
Presently, dental materials, such as e.g., MTA, Portland cement, are difficult to handle due to viscosity and slow setting times. These materials have low viscosity and therefore require special equipment to administer into small or tortuous areas in the patient's mouth.
U.S. Pat. Nos. 5,415,547, and 5,769,638 titled “Tooth Filling Material and Method of Use.” Teach the use of Portland Cement as a dental repair material for apicoectomy, a tooth cavity, correction of root perforation. Those patents also teach a method of performing a apicoectomy, a method for filling teeth and a method for sealing root perforations. It has also been observed that Portland Cement has similar properties to MTA as a dental repair compound.
International Patent Application WO 2005/039509 A1, titled “A Dental Composite Material and Uses Thereof” Teaches using a viscosity enhancing additive in Portland Cement. The application also teaches using the same viscosity enhancing substance to improve MTA as a workable dental repair material. However the description suggested enhancement of MTA. The viscosity enhancing substance is Polyvinyl alcohol, cellulose, cellulose derivatives, polyethylene oxide, natural gums, and/or aqueous clay dispersion.
The following references are cited throughout this section using the related parenthetical numbering system. The references are incorporated herein by reference. Applicant reserves the right to challenge the veracity of statements made therein.    1) Seux D, Regad C, Magloire H, Holz J. A model of an in vitro biological assay controlled by immunofluorescence and scanning electron microscopy. J Biol Buccale. 1991; 19:147-53.    2) Tziafas D, Pantelidou O, Alvanou A, Belibasakis G, Papadimitriou S. The dentinogenic effect of mineral trioxide aggregate (MTA) in short-term capping experiments. Int Endod J 2002; 35:245-54.    3) Pitt Ford T R, Torabinejad M, Abedi H R, Bakland L K, Kariyawasam S P. Using mineral trioxide aggregate as a pulp-capping material. J Am Dent Assoc 1996; 127:1491-4.    4) Faraco I M, Jr., Holland R. Response of the pulp of dogs to capping with mineral trioxide aggregate or a calcium hydroxide cement. 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